2 Answers

Vitamins, like Zinc and Carbos, boost your EVs by 10 a piece and raise happiness.

Battling wild Pokemon. All Pokemon have EV yields, like this Bidoofus. (1 HP EV). If you faint wild Pokemon, you get their EV yield. Here is every Pokemon's EV Yield.

Power Items, when held, give you 4 bonus EVs on fainting a Pokemon. So instead of Bidoofus giving you 1 HP EV, you get 5! However, different power items work for different stats. For example, Power Anklet works with Speed but not HP.

Macho Brace, when held, doubles EV gain on fainting a Pokemon. So instead of Bidoofus giving you 1 HP EV, you get 2 HP EVs. A Pokemon like Gengar that gives 3 SpAtk EVs, will give you 6 SpAtk EVs.

this link gives you information about everything needed. to sum up: you will gain EVs by beating a specific Pokemon. example: venusaur gives 3 EVs in sp.atk and nidoking gives Three EVs in attack. you can have 510 EVs in total. you can make EV training easier With giving Power items or vitamins. look at the link above for more details.